In-flight Wi-Fi is internet access for passengers on an aircraft, carried between the plane and satellites by an antenna on top of the aircraft. It is also called in-flight connectivity. Passengers connect their phones and laptops to the cabin Wi-Fi, as they would in a café.
The system has three parts. Inside the cabin, Wi-Fi access points in the ceiling connect the passengers' devices. A server on board links the access points to the antenna. On top of the plane, a flat antenna under a low cover sends and receives signals to and from a satellite. The satellite relays them to a ground station, which connects them to the internet. Some antennas can reach satellites in different orbits, both geostationary and low-orbit, as explained in LEO and GEO satellites.
In India, the government allowed in-flight Wi-Fi from 2018, and some airlines now offer it on domestic and international flights. Since late 2024, the rules allow Wi-Fi whenever passengers are permitted to use electronic devices on board. Mobile phone service on board is allowed only above 3,000 m, so that phones do not interfere with mobile networks on the ground.
Imagine a flight from Mumbai to Guwahati with 180 passengers. Once the crew allows electronic devices, the Wi-Fi switches on, and 60 passengers connect. The plane's satellite link carries, say, 50 megabits per second for the whole aircraft. So the system shares the link between the 60 devices. It lets messages and email through easily. It limits video streaming, because two or three films in high quality could use most of the link. A passenger replying to work emails over central India notices a short delay with each click. This is the time the signal takes to travel to a geostationary satellite and back, more than half a second.
Not every screen on board needs the internet. The films on the seat-back screens are stored on a server inside the aircraft. That is in-flight entertainment (IFE), and its films play even when the satellite link is down.
Who pays? The airline buys satellite capacity from a maritime and aviation satellite internet provider. It may give passengers Wi-Fi free, or charge for it by the flight. The antenna and modem on the roof are a kind of satellite terminal, built flat so that they add little air resistance.